Molybdenum is principally found in the earth's crust in the form of molybdenite (MoS.sub.2) ditributed as very fine veinlets in quartz which is present in an ore body comprised predominantly of altered and highly silicified granite. The concentration of the molybdenite in such ore bodies is relatively low, that is, in amounts of about 0.1% by weight, and more usually, about 0.5% by weight. The molybdenite is present in the form of relatively soft, hexagonal, black flaky crystals which are extracted from the ore body and concentrated by any one of a variety of known beneficiation processes so as to increase the molybdenum disulfide content to a level of usually greater than about 80% by weight of the concentrate. The resultant concentrate is subjected to an oxidation step, which usually is performed by a roasting operation in the presence of air, whereby the molybdenum disulfide is converted to molybdenum oxide which is of a commercial or technical grade containing various impurities including metallic contaminants present in the original ore body.
It is desirable or necessary in some instances to provide a molybdenum trioxide product or molybdate compounds which are relatively free of such metallic contaminants providing a high purity material for use in the preparation of molybdenum compounds, catalysts, chemical reagents or the like, wherein the presence of contaminants, such as compounds of potassium, manganese, lead, tin, calcium, magnesium, silicon, iron, copper and aluminum, is detrimental. The production of high purity molybdenum oxide has heretofore been achieved by various chemical and physical refining techniques, of which the sublimation of the technical oxide at an elevated temperature such as about 1000.degree.C or higher and recovering the sublimed molybdenum trioxide of a purity usually of about 99% or greater is perhaps the most common method. Unfortunately, the sublimation process is inefficient, producing a purified molybdenum trioxide in relatively low yields, necessitating a recycling and further processing of the residue to recover the residual molybdenum values therein, which still further detracts from the economics of the purification process.
Various chemical purification techniques, including multiple-stage leaching with various reagents, have heretofore been used or proposed for use which also have been unsatisfactory for one or more reasons. For example, selective leaching processes have been employed to which the technical oxide is subjected in a manner to selectively extract the major amounts of some of the contaminating constituents therein. A disadvantage of such plural leaching processes is the ineffectiveness of any one solution to remove substantially all of the deleterious naturally-occurring contaminating constituents in one step, necessitating a relatively tedious and time consuming plural leaching process which is not only costly and time consuming, but also results in a progressive reduction in the yield of the purified molybdenum product derived from the impure feed material.
The process of the present invention overcomes many of the problems and disadvantages associated with methods heretofore used or proposed for use enabling the production of relatively high purity ammonium dimolybdate and/or molybdenum trioxide in comparatively high yields and which utilizes processing conditions and equipment which are commercially efficient and economical.